Vinyl Plank on Old Wood Subfloor

[letra]

Hi Everyone,

This is my first post here...nice to meet you!

I am planning on putting vinyl plank down in my kitchen. I have the floor torn up with the subfloor exposed. The house was built in the 50s. The subfloor has old pine boards on the majority of it, and plywood down on one section. The plywood is probably 1/16th lower than the rest and I haven't checked it for level yet, but I'm sure it's not very level. Two pictures are attached.

I was hoping to get away without underlayment, but it seems like that might be necessary. My questions are these:

Do I need to put down underlayment?

If I do need to put down underlayment, what kind would you recommend and how should I secure it?

Thanks!

Scarlette

 

[Floorist]

Welcome. The vinyl plank guys will be along to answer your question.

 

[DarisMulkin]

I'm not a vinyl plank person but most of what I have resd is level isn't the issue, flat is. Read the instructions on your plank and it will tell you how flat in x amount of feet.

 

[Commercial Floor Rep]

Is it a click together product or is it a direct glue?

 

[letra]

Is it a click together product or is it a direct glue?

Click together.

 

[Commercial Floor Rep]

They will both require the same degree of flatness but for bonding purposes it would have required underlayment for sure to glue it down. Some flooring manufacturers will also state that strip wood like this isn't suitable and must have underlayment even though it's a click together product. What you got is pretty rough. If it were mine, I wouldn't chance it. I would just underlay it and move on. This will help increase the performance of the flooring long term by increasing strength and decreasing subfloor deflection from movement.

Vertical movement is a bad thing with click lock as it causes the lock mechanism to continually be bent back and forth every time it's walked on like breaking a twig and will either wear the locking mechanism out and cause it to unlock and separate or actually break the locking mechanism and cause separation. So, while a lot of dealers tout the ease of installation of the product itself, the floor prep is essentially the same requirement and the floor must be flat (not necessarily level).

The general ASTM requirements for any resilient flooring are no more than 3/16" in a 10' span in any direction or no more than 1/8" in a 6' span over any wood or concrete substrate. However, a manufacturer can require stricter tolerances if their product requires them. This is why it's always best to consult the manufacturer's written installation instructions as any problems for claims or warranty will be based upon those instructions not the industry standards unless the manufacturer doesn't address the particular issue in their instructions and then it defaults to the ASTM (read industry) standards.

 

[letra]

They will both require the same degree of flatness but for bonding purposes it would have required underlayment for sure to glue it down. Some flooring manufacturers will also state that strip wood like this isn't suitable and must have underlayment even though it's a click together product. What you got is pretty rough. If it were mine, I wouldn't chance it. I would just underlay it and move on. This will help increase the performance of the flooring long term by increasing strength and decreasing subfloor deflection from movement.

Vertical movement is a bad thing with click lock as it causes the lock mechanism to continually be bent back and forth every time it's walked on like breaking a twig and will either wear the locking mechanism out and cause it to unlock and separate or actually break the locking mechanism and cause separation. So, while a lot of dealers tout the ease of installation of the product itself, the floor prep is essentially the same requirement and the floor must be flat (not necessarily level).

The general ASTM requirements for any resilient flooring are no more than 3/16" in a 10' span in any direction or no more than 1/8" in a 6' span over any wood or concrete substrate. However, a manufacturer can require stricter tolerances if their product requires them. This is why it's always best to consult the manufacturer's written installation instructions as any problems for claims or warranty will be based upon those instructions not the industry standards unless the manufacturer doesn't address the particular issue in their instructions and then it defaults to the ASTM (read industry) standards.

Understood.

How thick should the plywood be for underlayment, and how should it be secured?

 

[Commercial Floor Rep]

Minimum 1/4" thickness and fastened following the panel manufacturers fastening schedule and pattern with a 1/4" crown 18 gauge galvanized chisel point staple that is long enough to penetrate the thickness of the underlayment and into the subfloor as far as possible without going through the subfloor completely on the bottom side. If it goes through completely you're essentially losing up to 1/2 of the holding power of the fastener. You should also regulate your air flow on your compressor so that the crown of the staple embeds into the underlayment so that's it's flush with the surface. If it's too sunk you'll risk blowing through the underlayment and have problems with it letting go.

General guidelines would be 2" along the edges and every 4 inches in the field. Many underlayments will come marked with a fastening pattern like the picture below. You should also follow the fastening pattern order as well starting in a corner like the picture below. This will prevent bowing and lifting. Your joints should be staggered so that you never have 4 corners coming together and the direction of the underlayment should be perpendicular to the direction of the subfloor below it to provide the greatest strength. Make sure you offset your joints so that they don't fall directly over the joints of the subfloor below as well. Do not use Luann as it typically does not meet the requirements for thickness, can have hidden voids in the panels and can also be dyed which can cause staining with certain types of floors.

 

[letra]

Minimum 1/4" thickness and fastened following the panel manufacturers fastening schedule and pattern with a 1/4" crown 18 gauge galvanized chisel point staple that is long enough to penetrate the thickness of the underlayment and into the subfloor as far as possible without going through the subfloor completely on the bottom side. If it goes through completely you're essentially losing up to 1/2 of the holding power of the fastener. You should also regulate your air flow on your compressor so that the crown of the staple embeds into the underlayment so that's it's flush with the surface. If it's too sunk you'll risk blowing through the underlayment and have problems with it letting go.

General guidelines would be 2" along the edges and every 4 inches in the field. Many underlayments will come marked with a fastening pattern like the picture below. You should also follow the fastening pattern order as well starting in a corner like the picture below as well. This will prevent bowing and lifting. Your joints should be staggered so that you never have 4 corners coming together and the direction of the underlayment should be perpendicular to the direction of the subfloor below it to provide the greatest strength. Make sure you offset your joints so that they don't fall directly over the joints of the subfloor below as well. Do not use Luann as it typically does not meet the requirements for thickness, can have hidden voids in the panels and can also be dyed which can cause staining with certain types of floors.

View attachment 14268

Thank you so much! If I'm putting down underlayment, can I ignore the slight dips between the boards and plywood sections of the subfloor? There's only about a 1/16 difference.

 

[Commercial Floor Rep]

You can kind of see in your pictures where someone else has "sort of" tried to patch along that meeting point previously. That old patch needs to be gone and you should use a cementitious floor patch to come out about a trowel width from that joint and ease the transition between the two. Their mistake was not coming out nearly far enough. Any large voids, depressions or humps should also be dealt with prior to underlaying with floor patch as needed. Otherwise, they will just telegraph through the new underlayment and you'll have to deal with them on top of new layer.

 

[highup]

I'd go thicker than one quarter inch. I've yet to see 1/4 inch underlayment grade plywood that it's remotely strong enough to do anything worthwhile. I'd go for at least 3/8 over a strip wood floor like that. I bet 3/8 thick plywood is at least twice as strong as the typical 1/4" underlayment grade junk that is sold these days. That said, quarter inch plywood isn't structural in the first place. It's kind of like putting on primer before the paint. 3/8" plywood is at least going to have some strength to it. That said, it might become more of a height issue if doors especially if outside doors are involved but I would say the thicker the better if you're going over much tongue and groove wood floor. The price might not be much different anyway between quarter and 3/8 plywood.